Understanding bears could help us survive heart attacks, researchers say

University of Minnesota researchers think lessons learned from hibernating black bears will help save human lives in a unique study that could someday improve the odds of surviving a heart attack.

Despite starving for four to six months, a bear's heart and other muscles remain strong and healthy, said Paul Iaizzo, a University of Minnesota professor who has studied hibernating bears for a dozen years. He is convinced that putting critically ill patients in the same sort of state of hibernation could save lives.

"You're trying to protect the vital organs and the loss of skeletal muscle," Iaizzo said. "And that's exactly what the bear will do here at the den. So they could be the ideal model for that [intensive care unit] patient."

Black bears are amazing physical specimens. They crawl into a hole in the ground in late fall. They don't eat or drink anything for four to six months. Then they climb out in the spring strong and healthy.

"We think there's a lot or really important clinical things we might learn that could apply to human medicine," Iaizzo said.

Earlier this spring, Iaizzo was in the northern Minnesota woods with other researchers gathering data on hibernating bears. He watched as Tim Laske, vice president for product development at the Medtronic medical devices company, set up portable imaging gear to look at the bear's heart.

Laske also downloaded data from a heart monitor inserted under the bear's skin months earlier. It showed how her heart changed as hibernation began.

"Her heart is slowed down, which is very typical for bears," Laske said. "We'll see the heart stop for 14 seconds at a time. If one of our hearts were to stop for even three seconds, you would faint."

During hibernation, a bear's heartbeat drops to five to 10 beats a minute. The heart rate speeds up to about 60 beats per minute when the bear takes a breath, then slows down again.

This data is unique because it tracks the bear's heart rate in its natural state. The data shows the bear's heart rate changes any time humans are nearby. So doing this research in a lab would likely mean inaccurate data.

Iaizzo recently performed open heart surgery on a pig at the University of Minnesota Visible Heart Lab in Minneapolis. Animals like it are used to test the effects of what Iaizzo calls hibernation factors.

In the labMPR Photo/Nikki Tundel

Researchers don't understand all of what's happening in a bear's body during hibernation, but Iaizzo said they are focused on hibernation induction triggers. One of those triggers is an opioid called delta opioid agonist, which seems to allow muscles to live with lower oxygen levels. The hibernation induction triggers circulating in a hibernating bear's blood are thought to protect its heart and other muscles during hibernation.

An infarct is the area of heart muscle that dies when it's starved of oxygen during a heart attack. Iaizzo wants to know what happens when pig hearts are treated with bear hormones before a heart attack.

"What we saw is they reduced the infarct size by 50 percent, which is really dramatic," he said. "We're looking at if you can induce the heart attack, then give the agents and see if you can minimize the damage. And this looks promising."

Those same hibernation agents could be used to protect the health of donor hearts during a heart transplant, Iaizzo said, improving the odds of success.

Iaizzo is also investigating how bears keep their muscle tone while lying around for four to six months during hibernation.

Paul IaizzoMPR Photo/Nikki Tundel

"Now if you or I were to sit around on a couch for a month and not do anything, we would lose up to 30 to 40 percent of our muscle mass."

That's just what happens to critically ill patients in hospitals. Iaizzo said sometimes they lose so much muscle mass they can no longer breathe on their own and need to be put on a ventilator. That muscle loss can also lead to organ damage.

"And this is a huge health care burden and cost," he said. "And we think some of what we're learning from these black bears could be applied in these clinical situations."

Iaizzo said the black bear still holds some medical mysteries. Researchers don't fully understand how its body stays so healthy during hibernation.

But he's confident what's been learned so far will lead to big improvements in medical care within the next 10 years.